This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Studying synthesis and repair of macromolecules in healthy humans is difficult. Above ground testing of nuclear weapons from 1955-1963 produced a large "bomb-pulse" of 14CO2, which was quickly distributed around the globe and intrinsically labeled all exchangeable carbon in the biosphere. Since the Test Ban Treaty in 1963, the atmospheric 14C bomb-pulse has been decreasing exponentially with a mean life of ~ 16 years, not due to radioactive decay, but due to diffusion and equilibration with the oceans and biosphere. All living humans have been labeled, and the 14C concentration in all organic macromolecules can sensitively identify when they were synthesized. In reality, we are all subjects in a long-term quasi-stable isotope tracer study in which molecular synthesis can be dated through the use of accelerator mass spectrometry (AMS) to count individual 14C atoms in sub-milligram samples. We seek to utilize this effective molecular chronometer to establish, quantify, and identify the specific nature of protein turnover in healthy adult human eye lenses. Preliminary data from lenses age 60 and greater suggests that the crystallin proteins of aged nuclear fiber cells contain carbon significantly younger than the cells themselves. This serves as direct evidence of in vivo protein turnover in human nuclear fiber cells and verifies the controversial hypothesis that the human eye lens maintains homeostasis at its core (at least in part) by de novo protein production. We will measure carbon turnover in purified proteins from the nuclear core of lenses formed after the peak of the bomb-pulse plus some aged controls. Compared with the data gathered from older donors, dating protein incorporation in younger lenses will provide direct evidence if this rate is attenuated when we reach middle age. A better understanding of lens maintenance could provide a useful new tool to understand and ultimately prevent the most common form of lens pathology, age related nuclear (ARN) cataract.